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Regulatory Assets and Liabilities (ROE of NSPI) (Details) - CAD ($) $ in Millions |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Nov. 29, 2016 | Jul. 19, 2016 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Phase-in Plan, Amount of Costs Deferred for Rate-making Purposes |  |  |  |  | $ 53 |
Regulatory Liabilities |  |  |  |  | 2,610 | $ 2,468
Regulatory Assets |  |  |  |  | $ 1,569 | $ 1,411
Public Utilities Act of Nova Scotia [Member] | Scenario, Forecast [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Settlement Amount |  |  |  | $ 111 |  |
Nova Scotia Power Inc. [Member] | Fuel Adjustment Mechanism Asset [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulated common equity component |  |  |  |  | 40.00% |
Nova Scotia Power Inc. [Member] | Rate Stability Plan fuel costs for 2017 through 2019 [Member] | Fuel Adjustment Mechanism Asset [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Approved average annual increase | 1.50% | 1.10% |  |  |  |
Nova Scotia Power Inc. [Member] | Public Utilities Act of Nova Scotia [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Settlement Amount, Minimum Contribution Amount |  |  |  | 10 | $ 10 |
Nova Scotia Power Inc. [Member] | Minimum [Member] | Fuel Adjustment Mechanism Asset [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  | 8.75% |
Nova Scotia Power Inc. [Member] | Maximum [Member] | Fuel Adjustment Mechanism Asset [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  | 9.25% |
NSP Maritime Link Inc. [Member] | Nova Scotia Power Inc. [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Settlement Amount, Actual Contribution Amount |  |  |  |  | $ 17 |
NSP Maritime Link Inc. [Member] | Scenario, Forecast [Member] | Nova Scotia Power Inc. [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities, Settlement Amount, Actual Contribution Amount |  |  | $ 53 | $ 36 |  |
NSP Maritime Link Inc. [Member] | Public Utilities Act of Nova Scotia [Member] | Nova Scotia Power Inc. [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public Utilities refunds payable to customers |  |  |  |  | 2 |
Public Utilities, Settlement Amount |  |  |  |  | $ 96 |

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